Name threads (#7879)

I noticed that [it's pretty easy to name threads in
Rust](https://doc.rust-lang.org/std/thread/#naming-threads). We might as
well do this; it's a nice quality of life improvement when you're
profiling something and the developers took the time to give threads
names.

Also added/cleaned up some comments while I was in the area.

crates/nu-command/src/core_commands/do_.rs

@@ -130,16 +130,21 @@ impl Command for Do {
                 // So we need a thread to receive stdout message, then the current thread can continue to consume
                 // stderr messages.
                 let stdout_handler = stdout.map(|stdout_stream| {
-                    thread::spawn(move || {
+                    thread::Builder::new()
+                        .name("stderr redirector".to_string())
+                        .spawn(move || {
                             let ctrlc = stdout_stream.ctrlc.clone();
                             let span = stdout_stream.span;
                             RawStream::new(
-                            Box::new(vec![stdout_stream.into_bytes().map(|s| s.item)].into_iter()),
+                                Box::new(
+                                    vec![stdout_stream.into_bytes().map(|s| s.item)].into_iter(),
+                                ),
                                 ctrlc,
                                 span,
                                 None,
                             )
                         })
+                        .expect("Failed to create thread")
                 });
 
                 // Intercept stderr so we can return it in the error if the exit code is non-zero.

crates/nu-command/src/filesystem/save.rs

@@ -8,6 +8,7 @@ use nu_protocol::{
 use std::fs::File;
 use std::io::{BufWriter, Write};
 use std::path::Path;
+use std::thread;
 
 use crate::progress_bar;
 
@@ -85,13 +86,17 @@ impl Command for Save {
 
                 // delegate a thread to redirect stderr to result.
                 let handler = stderr.map(|stderr_stream| match stderr_file {
-                    Some(stderr_file) => std::thread::spawn(move || {
+                    Some(stderr_file) => thread::Builder::new()
-                        stream_to_file(stderr_stream, stderr_file, span, progress)
+                        .name("stderr redirector".to_string())
-                    }),
+                        .spawn(move || stream_to_file(stderr_stream, stderr_file, span, progress))
-                    None => std::thread::spawn(move || {
+                        .expect("Failed to create thread"),
+                    None => thread::Builder::new()
+                        .name("stderr redirector".to_string())
+                        .spawn(move || {
                             let _ = stderr_stream.into_bytes();
                             Ok(PipelineData::empty())
-                    }),
+                        })
+                        .expect("Failed to create thread"),
                 });
 
                 let res = stream_to_file(stream, file, span, progress);

crates/nu-command/src/system/complete.rs

@@ -4,6 +4,8 @@ use nu_protocol::{
     Category, Example, IntoPipelineData, PipelineData, ShellError, Signature, Type, Value,
 };
 
+use std::thread;
+
 #[derive(Clone)]
 pub struct Complete;
 
@@ -50,7 +52,9 @@ impl Command for Complete {
                 let stderr_handler = stderr.map(|stderr| {
                     let stderr_span = stderr.span;
                     (
-                        std::thread::spawn(move || {
+                        thread::Builder::new()
+                            .name("stderr consumer".to_string())
+                            .spawn(move || {
                                 let stderr = stderr.into_bytes()?;
                                 if let Ok(st) = String::from_utf8(stderr.item.clone()) {
                                     Ok::<_, ShellError>(Value::String {
@@ -63,7 +67,8 @@ impl Command for Complete {
                                         span: stderr.span,
                                     })
                                 }
-                        }),
+                            })
+                            .expect("failed to create thread"),
                         stderr_span,
                     )
                 });

crates/nu-command/src/system/run_external.rs

@@ -18,6 +18,7 @@ use std::process::{Command as CommandSys, Stdio};
 use std::sync::atomic::AtomicBool;
 use std::sync::mpsc::{self, SyncSender};
 use std::sync::Arc;
+use std::thread;
 
 const OUTPUT_BUFFER_SIZE: usize = 1024;
 const OUTPUT_BUFFERS_IN_FLIGHT: usize = 3;
@@ -347,9 +348,17 @@ impl ExternalCommand {
                     // Turn off color as we pass data through
                     engine_state.config.use_ansi_coloring = false;
 
-                    // if there is a string or a stream, that is sent to the pipe std
+                    // Pipe input into the external command's stdin
                     if let Some(mut stdin_write) = child.as_mut().stdin.take() {
-                        std::thread::spawn(move || {
+                        thread::Builder::new()
+                            .name("external stdin worker".to_string())
+                            .spawn(move || {
+                                // Attempt to render the input as a table before piping it to the external.
+                                // This is important for pagers like `less`;
+                                // they need to get Nu data rendered for display to users.
+                                //
+                                // TODO: should we do something different for list<string> inputs?
+                                // Users often expect those to be piped to *nix tools as raw strings separated by newlines
                                 let input = crate::Table::run(
                                     &crate::Table,
                                     &engine_state,
@@ -372,7 +381,8 @@ impl ExternalCommand {
                                 }
 
                                 Ok(())
-                        });
+                            })
+                            .expect("Failed to create thread");
                     }
                 }
 
@@ -388,12 +398,14 @@ impl ExternalCommand {
 
                 let stdout = child.as_mut().stdout.take();
                 let stderr = child.as_mut().stderr.take();
+
                 // If this external is not the last expression, then its output is piped to a channel
                 // and we create a ListStream that can be consumed
-                //
+
-                // Create two threads: one for redirect stdout message, and wait for child process to complete.
+                // First create a thread to redirect the external's stdout and wait for an exit code.
-                // The other may be created when we want to redirect stderr message.
+                thread::Builder::new()
-                std::thread::spawn(move || {
+                    .name("stdout redirector + exit code waiter".to_string())
+                    .spawn(move || {
                         if redirect_stdout {
                             let stdout = stdout.ok_or_else(|| {
                                 ShellError::ExternalCommand(
@@ -462,11 +474,13 @@ impl ExternalCommand {
                             Ok(())
                         }
                     }
-                });
+                }).expect("Failed to create thread");
 
                 let (stderr_tx, stderr_rx) = mpsc::sync_channel(OUTPUT_BUFFERS_IN_FLIGHT);
                 if redirect_stderr {
-                    std::thread::spawn(move || {
+                    thread::Builder::new()
+                        .name("stderr redirector".to_string())
+                        .spawn(move || {
                             let stderr = stderr.ok_or_else(|| {
                                 ShellError::ExternalCommand(
                                     "Error taking stderr from external".to_string(),
@@ -478,7 +492,8 @@ impl ExternalCommand {
 
                             read_and_redirect_message(stderr, stderr_tx, stderr_ctrlc);
                             Ok::<(), ShellError>(())
-                    });
+                        })
+                        .expect("Failed to create thread");
                 }
 
                 let stdout_receiver = ChannelReceiver::new(stdout_rx);

crates/nu-protocol/src/pipeline_data.rs

@@ -5,6 +5,7 @@ use crate::{
 };
 use nu_utils::{stderr_write_all_and_flush, stdout_write_all_and_flush};
 use std::sync::{atomic::AtomicBool, Arc};
+use std::thread;
 
 const LINE_ENDING_PATTERN: &[char] = &['\r', '\n'];
 
@@ -726,8 +727,11 @@ pub fn print_if_stream(
     exit_code: Option<ListStream>,
 ) -> Result<i64, ShellError> {
     // NOTE: currently we don't need anything from stderr
-    // so directly consumes `stderr_stream` to make sure that everything is done.
+    // so we just consume and throw away `stderr_stream` to make sure the pipe doesn't fill up
-    std::thread::spawn(move || stderr_stream.map(|x| x.into_bytes()));
+    thread::Builder::new()
+        .name("stderr consumer".to_string())
+        .spawn(move || stderr_stream.map(|x| x.into_bytes()))
+        .expect("could not create thread");
     if let Some(stream) = stream {
         for s in stream {
             let s_live = s?;